The invention relates to a control device for a transmission which can be shifted automatically and manually in a motor vehicle, having a selector lever for setting at least the forward D, neutral N, reverse R, parking P positions and a position M for manual gearshifts, it being possible to activate a first and second tip switch in the position M for manual gearshifts, corresponding signals for manually shifting the transmission ratios up and down being output to a control unit in order to control the transmission via position sensors and control lines, and it being possible to determine a failure of the position sensors and/or of the control lines assigned to the position sensors.
The selector levers known previously in the prior art have the switch settings xe2x80x9c4xe2x80x9d, xe2x80x9c3xe2x80x9d, xe2x80x9c2xe2x80x9d and xe2x80x9c3 to 1xe2x80x9d for gearspeed limitation, for example for traveling downhill, said switch settings switching the transmission to the corresponding gearspeed. In the more recent selector levers known from the prior art, this gearspeed limitation is dispensed with to a certain extent if, namely, the transmission is embodied as an automated transmission and a tip switching activation is used. Here, the driver can shift the gearspeeds down manually via the tip gate and thus obtain the necessary engine brake effect when traveling downhill, for example. The tip switching connects a ground potential to an input of the control unit when the corresponding tip key or the corresponding tip switch is activated. These tip switches for the tip xe2x80x9cswitchingxe2x80x9d are generally Hall elements which are arranged in the gearshift cover and are activated or triggered by means of a magnet. It is problematic that at present optimum diagnostics cannot be carried out on these Hall switches, that is to say it is not possible to determine to an optimum degree whether these switches are operationally capable at a particular time so that for safety reasons it is not always possible to dispense with the corresponding gearspeed limitation.
In the prior art, DE-A-199 05 627 discloses a control device for a transmission in a motor vehicle which has a multiplicity of sensors, the sensors being arranged or provided at certain intervals in such a way that the different settings of the selector lever can be determined using these sensors. The intention is to increase the failsafeness of the sensor system with the arrangement of the multiplicity of sensors described here.
DE-A-41 35 362 discloses an electrical control device for an automatic transmission in which, in order to sense the position set at the selector lever, the various shift positions are detected by means of the arrangement of a plurality of contacts, after which a bit pattern is generated and processed by the electronic transmission control unit, it being possible to xe2x80x9ccorrectxe2x80x9d the position code in the case of simple faults.
In the prior art on which the invention is based, a control device is disclosed which is described in the non-prepublished patent application 199 38 528 and in which xe2x80x9cdynamic diagnosticsxe2x80x9d are carried out if the selector lever is moved outside the position M for manual gearshifts, namely outside the tip gate. For this purpose, Hall sensors are provided in the tip gate, respectively for the first and second tip switches and for the position M between the first and second tip switches which can be correspondingly triggered with a first permanent magnet assigned to a selector lever. In addition, a second permanent magnet is provided which is arranged at a specific distance from the first permanent magnet and which is secured to the shutter which covers the selector lever pivoting region. This second permanent magnet is arranged in such a way that, as it moves out of the parking P position into the reverse R position, it triggers the Hall sensor for the first tip switch (tip +), and, during the corresponding movement of the selector lever, the other Hall sensors are then sequentially triggered one after the other using this second permanent magnet. At the time when the Hall sensors are triggered in succession, test signals are transmitted to the control unit. A separately provided evaluation circuit with a sequence generator generates the corresponding signals here on the basis of the test signals which are present. At the time when all the Hall sensors are detected as being satisfactory, specifically when the corresponding frequency pattern is present, the selector lever can then be engaged from the forward D position into the position M for manual gearshifts. If the corresponding frequency pattern is not present after the xe2x80x9cdynamic diagnosticsxe2x80x9d of all the Hall sensors, it is detected that at least one Hall sensor or a control line which is assigned to this Hall sensor is in fact not functioning satisfactorily and an audible and/or visual warning signal for the driver is issued before the engagement of the selector lever into the position M for manual gearshifts, in order to indicate that the manual shift activations are not functioning here.
The xe2x80x9cdynamic diagnosticsxe2x80x9d of the known control device just described are not yet embodied in an optimum way. On the one hand, in the parking P position of the selector lever, it is not possible to diagnose whether all the Hall sensors or the control lines assigned to these Hall sensors are functioning satisfactorily. In the known control device, a dynamic sequential interrogation of the individual Hall sensors (position sensors) takes place, specifically only when the selector lever is correspondingly activated from the parking P position in the direction of the forward D position. If a fault has occurred, the driver can then be warned by the audible or visual warning signal only just before the forward D position is reached. This can lead to overhasty reactions of the driver if he already wishes to engage the position M for manual gearshifts and is only correspondingly warned at this time, specifically just in advance. On the other hand, with the known control device it is also not possible to detect possible short-circuits between the control lines in good time using the control unit. As a result, the embodiment of this known control device on which the invention is based is not yet optimum.
The invention is therefore based on the object of configuring and developing a control device of the type mentioned at the beginning in such a way that early warning for the driver of the vehicle is ensured as satisfactorily as possible and/or it is possible to check the control lines for short-circuits.
The object which is indicated in advance is then initially triggered with the features of the characterizing part of patent claim 1 by virtue of the fact that the control device is embodied in terms of circuit technology in such a way that, at least in the parking P or reverse R position of the selector lever, all the position sensors can be checked and the failure or short-circuit to xe2x80x9c+xe2x80x9d or a break in a line of a position sensor and/or of a control line can be determined. Furthermore, the previously indicated object is achieved by means of the features of the characterizing part of the independent patent claim 2 by virtue of the fact that the control device is embodied in terms of circuit technology in such a way that, in the neutral N or forward D position of the selector lever, a short-circuit to ground of the control lines assigned to the position sensors can be determined. Finally, the previously indicated object is achieved by means of the features of the characterizing part of the independent patent claim 3 by virtue of the fact that the control device is embodied in terms of circuit technology in such a way that, in the forward D position of the selector lever, all the position sensors can be checked and the failure of a position sensor and/or of a control line can be determined and/or the control device is embodied in terms of circuit technology in such a way that, in the parking P position, a short circuit to ground of the control lines assigned to the position sensors can be determined.
By means of the control device embodied according to the invention, there are now xe2x80x9cstatistical diagnosticsxe2x80x9d and not, as previously in the prior art, xe2x80x9cdynamic diagnosticsxe2x80x9d of the individual position sensors, in particular of the Hall sensors. In the state of rest of the motor vehicle, namely in the parked state, that is to say when the selector lever is in the parking P position, it is possible to check all the position sensors in the tip gate immediately when the driver activates the electrical system of the motor vehicle. The selector lever therefore no longer needs to be moved, as previously in the prior art, along the shift gate from the position P or R as far as the position D for checking of the position sensors to be able to take place in the tip gate. Consequently, a fault of the position sensors or of the control lines assigned to the position sensors is also detected at an early time so that the driver can also be warned early. Overhasty reactions of the driver when faults are diagnosed are avoided by this means. Furthermore, the control device according to the invention is embodied in terms of circuit technology in such a way that in the neutral N or forward D position of the selector lever, that is to say before the position M for manual gearshifts is reached, it is possible to check whether or not there is a short-circuit to ground [lacuna] which are assigned to the position sensors in the tip gate. In this way too, the driver of the motor vehicle can be warned promptly before the position M for manual gearshifts is engaged so that overhasty reactions are avoided. Finally, in a further embodiment, the control device is also embodied in terms of circuit technology in such a way that, in the forward D position of the selector lever, all the position sensors can be checked and the failure of a position sensor and/or of a control line can be determined, and, as a further alternative, the control device is embodied in terms of circuit technology in such a way that, in the parking P position of the selector lever, a short-circuit in the control lines assigned to the position sensors can be determined. As a result, the disadvantages described at the beginning are avoided by the control device according to the invention.
There are then a multiplicity of possible ways of advantageously configuring and developing the control device according to the invention. In this respect, firstly the patent claims which are dependent on patent claims 1, 2 and 3 can be referred to. In particular, a plurality of preferred embodiments of the invention will now be explained in more detail in the following description and the associated drawing.